Nuclear power plants and other heat-generating power plants such as coal, oil, and gas power plants, are normally equipped with a circulation system for water, in which steam which is generated in a reactor vessel or in a steam generator connected to the circulation system is passed to a steam turbine, from there to a condenser and condensate formed therein, after cleaning and preheating, is returned to the reactor vessel of the steam generator.
In operation of power plants of the above-mentioned kinds different corrosion products are formed in the circulation system, inter alia in the form of oxides containing one or more metals of the kinds included in construction materials in the circulation system such as, above all, iron and further, inter alia, nickel, cobalt, chromium, manganese, titanium, molybdenum, zinc and zirconium. The corrosion products occur both as ionic dissolved compounds and as particulate undissolved compounds. In those cases where a nuclear reactor vessel is part of the circulation system, the corrosion products will become radioactive. Besides being influenced by the temperature, the amount and the nature of the corrosion products are influenced especially by the pH value of the water and the concentration of hydrogen and oxygen dissolved in the water. The corrosion products are therefore indicators of important properties of the water. By continuously investigating the corrosion products, it can be determined whether changes in the corrosion environment have occurred which require action regarding the operation of the power plant to eliminate the cause of the changes, such as, inter alia, changes of the pH of the water and, if a nuclear reactor vessel is included in the circulation system, inter alia the degree of radioactive contamination in the circulation system and the degree of oxide growth of cladding material for the fuel and of box material. It is, of course, of decisive importance for the operation of a power plant of the above-mentioned kinds that the water in the circulation system is as clean as possible to counteract the occurrence of corrosive coatings and an ensuing deteriorated economy.
When it comes to determining the chemical composition and the content of ionic dissolved compounds in water in water circulation systems of the kind described, automatic sampling systems have been produced, with the aid of which the nature and content of ionic compounds can be continuously followed during operation of the power plant. For analysis of particulate compounds, no corresponding automatic technique has been available. It has been necessary to separate the particulate compound from samples taken of the water on filters and then to determine the compounds by conventional methods by measuring directly on the filter or by dissolving the compounds in a solvent in a separate operation and analyzing the solution thus obtained in another separate operation. For analysis of this solution, a great number of methods can be used. In those cases where the analysis sensitivity is too low, the contents in the solution can be increased by using for analyses a larger water sample and hence a longer filtering time (enrichment time). Determination methods for solid samples for direct measurement of the particulate compounds on the filter are not applicable to water in water circulation systems of the kind described because of insufficient sensitivity.
According to the present invention, particulate compounds can be determined automatically in a sampling system in a reliable and simple manner, which includes a filtering of samples from the water in water circulation systems of the above-described kind or of liquid flows of another kind as well as dissolution of the particulate compounds, collected on the filter, in a solvent and determination of the nature and content of one or more of the particulate compounds in the solution obtained. For the dissolution known solvents for the particulate particles in question are used, and for analysis of the solution known analysis methods are used.
The invention is applicable not only to the analysis of particulate compounds in water in water circulation systems in power plants of the kinds described in the introduction, but also to the determination of particulate compounds in water of another kind and in liquids of another kind, such as spirit solutions and solutions of organic solvents, to the extent that these contain particulate compounds.
The present invention relates to a method of determining the chemical composition and the content of one or several particulate compounds in a flow of a liquid, whereby samples of the liquid are taken out from the flow and particulate compounds in the sample taken are collected on a filter through which the liquid in the sample is caused to pass, whereafter the collected particulate compounds are dissolved in a solvent while forming a solution in which the chemical composition and the amount of one or more of the particulate compounds are determined, characterized in that the filter is arranged in a closable container of a material permeable to microwaves; that samples of a fixed size of the liquid in the flow are supplied batchwise to the container on one side of the filter via an openable and a closable connection between the liquid flow and the container; that liquid, having passed through the filter, from each liquid sample supplied batch-wise is discharged from the container via an openable and a closable outlet on the other side of the filter; that after closing of the connection between the liquid flow and the container and of the outlet for the liquid having passed through the filter, a fixed amount of the solvent for the particulate compounds is supplied via an openable and a closable inlet to the container with particulate compounds from each liquid sample, supplied batchwise, collected on the filter and with the liquid from the liquid sample, supplied batchwise, discharged from the container; that the collected particulate compounds from each liquid sample, supplied batchwise, are dissolved in the solvent while heating the contents of the container by a microwave field from a microwave oven in which the container is arranged; and that the solution of the particulate compounds, thus obtained, in each liquid sample supplied batchwise is discharged via an openable and a closable outlet to an analysis apparatus, in which the composition and the content of one or more of the particulate compounds are determined.
The filter consists of a material which is resistant to the liquid to be analyzed and to the used solvent. Among suitable materials may be mentioned polytetrafluoroethylene and other fluorinated hydrocarbon polymers, for example polychlorotrifluoroethylene, as well as other resistant resins; further, inter alia, porcelain filters and sintered resistant particulate materials, for example sintered glass filters. The hole size of the filter is chosen in view of the size of the particulate compounds in the liquid flow. In most cases a hole size within the interval 0.2 .mu.m-1.0 .mu.m is suitable.
The container of a material permeable to microwaves also consists of a material which is resistant to the liquid to be analyzed and to the used solvent. Among suitable materials may be mentioned polytetrafluoroethylene and other fluorinated hydrocarbon polymers, for example polychlorotrifluoroethylene and glass. The volume of the container may suitably amount to 5-50 ml.
The particulate compounds are collected on the filter for a certain period of time. The time is chosen, depending on the particle content, such that a suitable amount of particles are collected on the filter. This amount should be such that it is suitable for analysis of the solution of the dissolved particulate compounds.
The solvents which are used for dissolution of the particulate compounds collected on the filter are, of course, dependent on the nature of the particulate compounds. For dissolution of corrosion products in water in a water circulation system in a nuclear power plant, as well as in other power plants of the kind described above, mixtures of acids may be used, preferably oxidizing such mixtures, as well as formers of chelate complexes. Mixtures of acids can be used for decomposition of most types of corrosion products of the kind described, whereas chelate formers are more specific. The chelate solutions usually have an optimum pH for dissolution in the interval 2-8. As examples of useful mixtures of acids may be mentioned mixtures of at least two of the acids hydrochloric acid, nitric acid, and perchloric acid. As examples of useful formers of chelate complexes may be mentioned ethylenediaminotetra acetic acid, citric acid and thioglycolic acid (HS--CH.sub.2 --COOH). The latter is particularly effective in mixtures with hydrochloric acid.
The time for dissolving a sample of particulate compounds varies with the sample quantity, the sample composition, the sample structure, the degree of atomization, the temperature, and the strength, pH and composition of the mixture of acids or the chelate solution. By heating the sample by microwaves, the rate of dissolution may be greatly reduced, from the order of magnitude of hours without microwave heating to the order of magnitude of minutes with microwave heating. The increased rate is assumed to be due to an increased convection in the solution and to an absorption of energy directly and locally in the grains of the particulate material.
The analysis of the solution of the particulate compounds is performed with known methods, for example by ion chromatography or by atom absorption spectrometry.
The method according to the invention operates on line, i.e., the sampling equipment used is connected to the liquid flow in which the nature and content of the particulate compounds are to be analyzed. All measures, such as opening and closing of valves, heating processes and times for different operations, are controlled by automatic control, preferably by computer control, for example comprising the use of microprocessors. In this way, a series of results is obtained from each sample taken batchwise from the liquid flow, thus obtaining an automatic determination of the particualte compounds for the whole of the time during which the determination is carried out.